272.

Discuss the salt hydrolysis in the following cases:
(i) Salts of strong acid and strong base
(ii) Salts of strong acid and weak base
(iii) Salts of weak acid and strong base
(iv) Salts of weak acid and weak base.

(i) Salts of strong acid and strong base:
When a salt of the strong acid and a strong base (say NaCl) is dissolved in water, the resulting solution is neutral having pH equal to 7. The hydrolysis of the salt can be represented as:

i.e. there is the only dissociation of sodium chloride and no hydrolysis.

(ii) Salts of strong acid and weak base:
When a salt of the strong acid and a weak base is dissolved in water, it gives an acidic solution having pH value less than 7. For example hydrolysis of NH₄Cl can be represented as:

   



The overall reaction will be


i.e. it is a cationic hydrolysis.

(iii) Salts of weak acid and strong base:
When a salt of weak acid and a strong base is dissolved in water, it gives a basic solution having pH greater than 7. For example hydrolysis of sodium acetate can be represented as:


   The overall reaction will be

 

i.e. it is an anionic hydrolysis.

(iv) Salts of weak acid and weak base:
When a salt of weak acid and a weak base is dissolved in water, it forms an almost neutral aqueous solution having value almost equal to 7. For example, hydrolysis of ammonium acetate can be represented as:


The overall reaction will be

i.e. it involves both anionic as well as cationic hydrolysis.